1. STABILIZING WORLD POPULATION
THE HUMAN POPULATION
STABILIZING WORLD POPULATION
Population Ecology & Human Population

2. WHAT IS POPULATION ECOLOGY:
population – collection of individuals of same species in a given area whose members can breed with one another
population ecology studies
dynamics of species’ populations
how these populations interact with environment
Population Ecology & Human Population

3. WHAT IS POPULATION ECOLOGY:
3 important characteristics of a population are its:
geographic distribution - describes area inhabited by a population
population density = # of individuals
unit area2
growth rate - increase or decrease of # individuals in a population over time
Population Ecology & Human Population

4. Population Ecology & Human Population
population changes
global scale: change in population is due to # of births & deaths
local populations: change in population is due to # of births, deaths, immigration (i), & emigration (e)
Population Ecology & Human Population

5. WHAT IS POPULATION ECOLOGY:
growth rate (r) – rate of change (increase or decrease) of a population’s size, expressed in %/yr
growth rate = birth rate - death rate
r = b - d
Population Ecology & Human Population

6. Maximum Population Growth
Biotic potential: maximum rate of increase under ideal conditions and affected by factors called life history characteristics
Life history characteristics
Age at first reproduction
Reproductive fraction of life span
Number of reproductive periods/events
Number of offspring per reproductive event
Large organisms (whales, elephants) have lesser biotic potentials
Small organisms (microorganisms) have greater biotic potentials
Population Ecology & Human Population

7. Reproductive Patterns and Survival
Population Ecology & Human Population

8. Population Ecology & Human Population
R-ADAPTED SPECIES
short life
rapid growth
early maturity
many small offspring
little parental care
little investment in individual offspring
adapted to unstable environment
pioneers, colonizers
niche generalists
Prey
regulated mainly by extrinsic factors
low trophic level
Population Ecology & Human Population

9. Population Ecology & Human Population
K-ADAPTED SPECIES
long life
slower growth
late maturity
fewer large offspring
high parental care & protection
high investment in individual offspring
adapted to stable environment
later stages of succession
niche specialists
predators
regulated mainly by intrinsic factors
high trophic level
Population Ecology & Human Population

10. EXPONENTIAL GROWTH: J-SHAPED
When bacteria divide at a constant rate & their #s are graphed, curve of exponential population growth has a characteristic J shape
Streptococcus
bacteria cell dividing
exponential population growth – accelerating population growth that occurs when optimal conditions allow a constant reproductive rate
Population Ecology & Human Population

11. EXPONENTIAL GROWTH: J-SHAPED
under ideal conditions with unlimited resources, population will grow exponentially
occurs when individuals in a population reproduce at a constant rate
exponential growth curve –
(J-shaped) graph that shows
phase of population growth
during which size of population
doubles regularly within a
certain time period
Population Ecology & Human Population

12. LOGISTIC GROWTH: S-SHAPED CURVE
logistic growth curve
most populations go
through a # of growth
phases, which can be
represented on a logistic
growth curve.
steady state – portion of a logistic growth curve in which the average growth rate is zero
Population Ecology & Human Population

13. LOGISTIC GROWTH: S-SHAPED CURVE
exponential growth does
not continue for very long
as resources become less
available, growth of a
population slows or stops
occurs when a population's growth slows or stops following a period of exponential growth.
Population Ecology & Human Population

14. LOGISTIC GROWTH: S-SHAPED CURVE
carrying capacity (K) – largest population a particular environment can support sustainably (long-term) assuming that there are no changes in that environment
Paramecium is a unicellular protist, a kind of microorganism
Population Ecology & Human Population

15. Population Ecology & Human Population
CARRYING CAPACITY
carrying capacity – size of population during steady state portion of logistic growth curve
largest # of individuals of a population that an environment can support sustainably
when a population reaches carrying capacity (K), its growth levels off
average growth rate= zero
# varies from species to species.
Population Ecology & Human Population

16. Population Ecology & Human Population
CARRYING CAPACITY
Population Ecology & Human Population

17. environmental
resistance
carrying capacity (K)
population stabilizes
Population size
exponential
growth
biotic
potential
Time (t)

18. Number of sheep (millions)
2.0
Population
overshoots
carrying
capacity
Carrying capacity
1.5
Population recovers
and stabilizes
Population
runs out of
resources
and crashes
Number of sheep (millions)
1.0
Exponential
growth .5
Figure 5.12
Logistic growth of a sheep population on the island of Tasmania between 1800 and After sheep were introduced in 1800, their population grew exponentially, thanks to an ample food supply. By 1855, they had overshot the land’s carrying capacity. Their numbers then stabilized and fluctuated around a carrying capacity of about 1.6 million sheep.
1800
1825
1850
1875
1900
1925
Year
Fig. 5-12, p. 111

19. 2,000 Population overshoots carrying capacity 1,500 Population crashes
Number of reindeer
1,000
500
Carrying
capacity
Figure 5.13
Exponential growth, overshoot, and population crash of reindeer introduced to the small Bering Sea island of St. Paul. When 26 reindeer (24 of them female) were introduced in 1910, lichens, mosses, and other food sources were plentiful. By 1935, the herd size had soared to 2,000, overshooting the island’s carrying capacity. This led to a population crash, when the herd size plummeted to only 8 reindeer by Question: Why do you think this population grew fast and crashed, unlike the sheep in Figure 5-12?
1910
1920
1930
1940
1950
Year
Fig. 5-13, p. 112

20. WHAT IS POPULATION ECOLOGY:
survival of a species depends on how well it can (as a group)
reproduce
utilize available resources
adapt to a changing environment
Population Ecology & Human Population